1. Field of the Invention
The present invention relates to an improvement in fiber-reinforced resin composite materials used as printed circuit boards for electronic equipment, etc.
2. Statement of the Prior Art
Heretofore, laminated sheets obtained by the hot-pressing lamination of a predetermined number of resin-impregnated sheetings formed by impregnating glass cloth with a fluororesin and melting it by heating have been used for electrical purposes. For such laminated sheets, laminated sheets obtained by the deposition of greige goods onto said glass cloth are disclosed in Japanese Patent Laid-Open (Kokai) Publication Nos. 60(1985)-240743 and 62(1987)-161538.
Use of such greige goods-deposited glass cloth gives laminated sheets having a reduced or limited degree of water absorption and an increased insulation resistance after hygroscopic treatments.
Originally, the above greige goods have been used for the purpose of bonding monofilaments together when preparing glass fibers by putting them into yarn or strand. Generally used for this are polyvinyl alcohol, starch, fats and oils, etc.
However, later studies have revealed that said greige goods have an adverse influence mainly upon insulation resistance and offer problems such as a lowering of moisture absorption resistance and carbonization of fluororesins during firing. In order to provide a solution to such problems, it is now under investigation to use cloth from which the above greige goods are removed by heat cleaning or wet washing or to treat such cloth with various coupling agents such as those based on silanes, chromium and titanium. A coupling treatment with an aminosilane is now found to be especially preferred for a composite material comprising a combination of inorganic fiber materials with fluororesins. Indeed, such a composite material is on practical levels in wide applications.
However, there is left much to be desired for the above composite material comprising a combination of inorganic fiber materials with fluororesins, since it is still less than satisfactory in terms of moisture absorption resistance so that its insulation resistance is likely to drop due to moisture absorption.